In a recent paper Morrison and Feldt1 (MF) discussed the ambiguities that occur during the practical implementation of scattering theories. They specifically mentioned the sometimes ambiguous implementation of the relationship between the S and T operators [defined by MF (4) and MF (26), respectively]. The correct relationship is given (in matrix form) by MF (28), which is sometimes written in the form S=12πiT [MF (31)]. MF write: “This operator form implies that the momentum-space T-matrix elements must contain (in the second term) both the delta function δ(EkEk) and the on-shell restriction.”

As an example, we draw attention in this Note to such an ambiguity in a standard reference text by Blum, Density Matrix Theory and Applications,2 which has played a historically significant role as a basic reference for coherence parameter studies...

AAPT members receive access to the American Journal of Physics and The Physics Teacher as a member benefit. To learn more about this member benefit and becoming an AAPT member, visit the Joining AAPT page.